The last working reactor in Japan is to be switched off Saturday, leaving the country without nuclear power just over a year after the world's worst atomic accident in a quarter of a century.

This aerial view, taken in 2010 shows the the Tomari nuclear plant in northernmost Hokkaido, northern Japan.

As technicians ready to close down the No. 3 unit at Tomari in Hokkaido, the debate over whether Japan needs nuclear power has been reignited, amid increasingly shrill warnings of summer power blackouts.

Hokkaido Electric Power, which runs the plant, said they would at 5pm (0800 GMT) begin inserting control rods that would halt the chain reaction and bring the reactor to "cold shutdown" some time on Monday.

The shuttering will mark the first time since the 1970s that resource-poor and energy-hungry Japan has been without nuclear power, a technology that had provided a third of its electricity until meltdowns at Fukushima.

The tsunami-sparked disaster forced tens of thousands of people from their homes in an area around the plant -- some of whom may never be allowed to return.

It did not directly claim any lives, but has devastated the local economy, leaving swathes of land unfarmable as radiation spewed from the ruins.

With the four reactors at Fukushima crippled by the natural disaster public suspicion of nuclear power grew, so much so that no reactor shut for routine safety checks has since been allowed to restart.

When the fission reaction stops in the middle of Saturday night, Japan's entire stable of 50 reactors will be offline, despite increasingly urgent calls from the power industry and bodies like the OECD, who fear dire consequences for the world's third largest economy.

Last month, Kansai Electric Power, which supplies mid-western Japan, including the commercial hubs of Osaka, Kyoto and Kobe, said a hot summer could see supply fall nearly 20 percent short of demand.

Kyushu Electric Power, covering an area further west, as well as Hokkaido Electric Power also said they will struggle as air conditioning gets cranked up in Japan's sweltering summer.

Kansai Electric last month booked a $3 billion annual loss, turning around a $1.5 billion profit the year earlier on the increased cost of using previously mothballed thermal fuel plants.

A week earlier, Prime Minister Yoshihiko Noda's government gave the green light to restarting reactors at the Oi nuclear plant, run by Kansai Electric, but regulators still have to convince those living near the plant.

In order to be fired up again, reactors must now pass International Atomic Energy Agency-approved stress tests and get the consent of their host communities -- it is this last hurdle that is proving hardest to overcome.

Critics of nuclear power say Japan has managed thus far with its ever dwindling pool of reactors and need not look back.

Environmental campaign group Greenpeace said Friday the country should concentrate on ramping up renewables and boosting energy efficiency.

"Despite the closure of all reactors, security of electricity supply is not threatened in Japan," said Hisayo Takada, Greenpeace Japan Climate and Energy Campaigner.

"The 2012 summer peak in electricity demand can be managed with energy efficiency, proper load balancing, and energy conservation."

Takada said recent warnings that another big earthquake could strike seismically volatile Japan at any time meant the technology was not to be trusted.

"Should another meltdown occur, it is likely that it will break the back of Japan's economy, and many more people will suffer. It is simply not worth the risk when the clean and safe alternative of renewable energy is at our fingertips."